Changing 3 blade prop to 5 blade on Mercury 225 Optimax- can it cause a rattle in gearbox

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EnzoCavallini

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We have recently purchased a Mercury 225 optimax fitted onto a Ruzi2000 Hull.

It had a 3 blade Mercury Prop on and we changed it to a High five 5 blade and a strange rattling noise started coming from the gearbox.
We also noticed the revs increased to over 5000rpm with the 5 blade prop and the rattling sound was around 4000rpm.

We have since put the 3 blade prop back on and the sound from the gearbox has gone.

Is this 5 blade prop the cause or do we have a problem in the drive train?
 

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What did you want to achieve by switching to a HighFive?

The engine should reach 5000-5750 rpm at WOT (Wide Open Throttle) with normal load (boat gross weight with all crew and stuff). If it doesn't you need a lower pitch propeller. By rule of thumb (and everything else is OK) one inch less pitch gives you 200 more rpm at WOT.

If same pitch the HighFive would get the same or slightly less rpm (due to 5 blades having more resistance in the water)

The rpm raise and noise makes one think that it wasn't properly fitted or the hub kit wasn't correct/intact

Propellers-5.jpg
 
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At a guess, I would think it wasn't properly fitted or the hub kit wasn't right. Was it the correct high 5 prop for the larger gear case you have ? there is one that is for the smaller gear case too.
Going from a good 3 blade stainless to a high 5 of the same pitch, almost always results in higher rpm at the top end (and noticeably less speed and fuel economy). The prop slip from these at the top end is horrendous. The only thing they are good for is low down acceleration for water sports. Terrible at everything else.
Check the hub kit that is in it, but there is also a good chance you may have tightened it down against the locking washer, slightly off alignment. this can cause some play
 
QBhoy said:
At a guess, I would think it wasn't properly fitted or the hub kit wasn't right. Was it the correct high 5 prop for the larger gear case you have ? there is one that is for the smaller gear case too.
Going from a good 3 blade stainless to a high 5 of the same pitch, almost always results in higher rpm at the top end (and noticeably less speed and fuel economy). The prop slip from these at the top end is horrendous. The only thing they are good for is low down acceleration for water sports. Terrible at everything else.
Check the hub kit that is in it, but there is also a good chance you may have tightened it down against the locking washer, slightly off alignment. this can cause some play
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Thanks for the response, let me test it again , will check the hub kit is suited to the gear case, I personally am not a fan changing as the 3 blade seems to be perfect for top end and torque to pull us up water skiing
 
ChromeDome said:
Well, on my Sea Ray the HighFive performed very well when grip was needed (esp. turns) and when engine was raised.
Laser II got the better lift and top speed.

If interested Quicksilvers 64 pages booklet "Everything_you_need_to_Know_about_propellers" can be dowloaded here
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Thanks for the booklet, I will start browsing through it
 
EnzoCavallini said:
Thanks for the response, let me test it again , will check the hub kit is suited to the gear case, I personally am not a fan changing as the 3 blade seems to be perfect for top end and torque to pull us up water skiing
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No probs...Having been obsessed by props for far too long and spent far too much money on them over the years, I might suggest that unless you are almost exclusively wake boarding or towing...and with a boat that's a little underpowered for it...there shouldn't be ever a need for a high 5 prop. I am a firm believer that there isn't much a really good and well suited 3 blade can't achieve these days. You won't be lacking power with that engine. I might also urge you to take advantage of the rpms you have to play with. That engine can rev into the late 5000's as far as I know. Not too familiar with your hull though. What pitch is the High 5 you put on it ? what pitch is the 3 blade and what type is it ? The engine and gear case you have has a wonderful range of props available for it. Props like the tempest plus and enertia are astonishing props.
 
ChromeDome said:
WOT range is 5000-5750 so should aim for the upper limit of that to get max hp and and acceleration.

The hulls seems to be an African (Zimbabwe?) flats design?
Sounds exotic, might be wrong
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looks like a quick machine...be a crying shame to have a 5 blade on that..
 
ChromeDome said:
Made this some years ago.

Norwegian Enos 17 console with 225 hp Merc. 111 kph. On a balance :)

Box
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Can't seem to open that, but sounds tasty...always loved a fast boat. Had a few over the years and still have two quick machines tucked away presently. One of them should break the 70 mph barrier this season with a prop change...the other is just short of the mark. All good fun ! I will need to look up the Enos...love a Scandinavian boat..especially the fjordling !
 
Several interesting designs in Scandinavia back then. Finnish Flipper with staged hull aft, Wesling with the unique balast keel that at still it takes in water to keep it stable, at hole shot it empties and goes fast. And the Norwegian Dromedille by Bror With. Not to mention Hydrolift, also Norwegian.
And Coronet from Denmark.

Edit: Almost forgot the Swedish Smuggler. Gone now, but the Finnish Segmo builds on the same.

Ingenious Wesling:

IMAG0437.jpg.64a1c39525af6f12efaebaefd04df861.jpg
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